State-of-the-art matrix-assisted laser desorption time-of-flight (MALDI-TOF) and bench-top electrospray ionization (ESI) mass spectrometers will be purchased to further the research of the facility, postdoctoral associates, and graduate students in the Departments of Chemistry, Biochemistry, and Cell and Structural Biology. The systems will be used for the study of biological macromolecules of high molecular weight. There are a series of important measurements that cannot be undertaken with current mass spectrometers, and so this purchase becomes enabling for a wide range of projects. The new instruments will be housed in the School of Chemical Sciences in its Mass Spectrometry laboratory. The major users of the systems will be M. Gillette to study the roles of peptides in the brain~s biological clocks, J.A. Katzenellenbogen to analyze ligand-induced conformational changes and phosphorylation in estrogen receptors, D. Kranz to investigate the control of T-cell activity with peptide/protein agonists and antagonists, J.S. Moore to characterize structure-controlled macromolecules, K.L. Rinehart to advance high resolution biological mass spectrometry, K.S. Suslick to study heme proteins and metalloporphyins, and J.V. Sweedler to investigate the distribution of peptides throughout the cellular processes of individual neurons. Prof. Sligar, although only a minor user of proposed instruments, is the director of the School of Chemical Sciences at the University of Illinois and therefore is the Principal Investigator of this proposal.